In 1955
Eastman Kodak used Mylar as a support for photographic film and called it "ESTAR Base".[5] The very thin and tough film allowed 6,000-foot (1,800 m) reels to be exposed on long-range
U-2 reconnaissance flights.[6]
In 1964,
NASA launched
Echo II, a 40-metre (131 ft) diameter balloon constructed from a 9-micrometre (0.00035 in) thick mylar film sandwiched between two layers of 4.5-micrometre (0.00018 in) thick aluminium foil bonded together.[7]
Manufacture and properties
The manufacturing process begins with a film of molten
polyethylene terephthalate (PET) being
extruded onto a chill roll, which quenches it into the amorphous state.[8] It is then biaxially oriented by
drawing. The most common way of doing this is the sequential process, in which the film is first drawn in the machine direction using heated rollers and subsequently drawn in the transverse direction, i.e.,
orthogonally to the direction of travel, in a heated oven. It is also possible to draw the film in both directions simultaneously, although the equipment required for this is somewhat more elaborate. Draw ratios are typically around 3 to 4 in each direction.
Once the drawing is completed, the film is "
heat set" or
crystallized under tension in the oven at temperatures typically above 200 °C (392 °F). The heat setting step prevents the film from shrinking back to its original unstretched shape and locks in the molecular orientation in the film plane. The orientation of the polymer chains is responsible for the high strength and stiffness of biaxially oriented PET film, which has a typical
Young's modulus of about 4 GPa (0.58×10^6 psi). Another important consequence of the molecular orientation is that it induces the formation of many crystal nuclei. The crystallites that grow rapidly reach the boundary of the neighboring crystallite and remain smaller than the wavelength of visible light. As a result, biaxially oriented PET film has excellent clarity, despite its
semicrystalline structure.
If it were produced without any additives, the surface of the film would be so smooth that layers would adhere strongly to one another when the film is wound up, similar to the sticking of clean glass plates when stacked. To make handling possible, microscopic inert inorganic particles, such as
silicon dioxide, are usually embedded in the PET to roughen the surface of the film.[9]
Biaxially oriented PET film can be
metallized by
vapor deposition of a
thin film of
evaporatedaluminium,
gold, or other metal onto it. The result is much less permeable to gases (important in
food packaging) and reflects up to 99% of light[citation needed], including much of the
infrared spectrum. For some applications like food packaging, the aluminized boPET film can be laminated with a layer of
polyethylene, which provides
sealability and improves
puncture resistance. The polyethylene side of such a laminate appears dull and the boPET side shiny.
Uses for boPET polyester films include, but are not limited to:
Flexible packaging and food contact
Laminates containing metallized boPET foil (in technical language called printin[check spelling] or laminate web substrate) protect food against oxidation and aroma loss, achieving long
shelf life. Examples are coffee "foil" packaging and pouches for convenience foods.
Pop-Tarts are sold in pairs wrapped in silver boPET. They were previously wrapped in foil.
White boPET web substrate is used as lidding for dairy goods such as
yogurt.
Clear boPET web substrate is used as lidding for fresh or frozen ready meals. Due to its excellent heat resistance, it can remain on the package during microwave or oven heating.
boPET film is used in bagging
comic books, in order to best protect them during storage from environmental conditions (moisture, heat, and cold) that would otherwise cause paper to slowly deteriorate over time. This material is used for
archival quality storage of documents by the
Library of Congress (Mylar type D, ICI Melinex 516 or equivalent)[10][11] and several major library comic book research collections, including the Comic Art Collection at
Michigan State University.[12] While boPET is widely (and effectively) used in this archival sense, it is not immune to the effects of fire and heat and could potentially melt, depending on the intensity of the heat source, causing further damage to the encased item.[13]
Similarly,
trading card decks (such as Pokémon, Magic: The Gathering, and Yu-Gi-Oh!) are packaged in pouches or sleeves made of metallized boPET. It can also be used to make the holographic artwork featured on some cards, typically known as "holos", "foils", "shinies", or "holofoils".
For protecting the spine of important documents, such as
medical records.
Translucent Mylar film, as wide as 48" and in up to 12' in length, found widespread use as a non-dimensional engineering drawing media in the aerospace industry due to its dimensional stability (also see Printing Media section below). This allows production and engineering staff to lay manufactured parts directly over or under the drawing film in order to verify the fidelity of part profiles, hole locations and other part features.[14]
Metallized boPET
solar curtains reflect sunlight and heat away from windows.
Aluminized, as an inexpensive
solar eclipse viewer, although care must be taken, because invisible fissures can form in the metal film, reducing its effectiveness.
Amateur and professional visual and telescopic
solar filters. BoPET films are often annealed to a glass element to improve thermal conductivity, and guarantee the necessary flat surface needed for even telescopic solar observation. Manufacturers will typically use films with thicknesses of 280–500 micrometres (0.011–0.020 in), in order to give the films better resilience. 250-micrometre (0.0098 in) thickness films with a heavy aluminium coating are generally preferred for naked-eye Solar observation during eclipses.
Films in annular ring mounts on gas-tight cells, will readily deform into spherical mirrors.
Photomultipliercosmic-ray observatories often make use of these mirrors for inexpensive large (1.0 m and above), lightweight mirror surfaces for sky-sector low and medium energy cosmic ray research.
As a light diaphragm material separating gases in hypersonic shock and expansion tube facilities.
Insulating material for a cryocooler radiation shield.
As a window material to confine gas in detectors and targets in
nuclear physics.
In
CT scanners it acts as a physical barrier between the X-ray tube, detector ring and the patient allowing negligible attenuation of the X-ray beam when active.
Spacecraft are insulated with a metallized BoPET film.
The descent stage of the
Apollo Lunar Module was covered with BoPET to control the temperature of equipment for lunar exploration carried in the Modular Equipment Stowage Assembly.
BoPET film has been used in the production of
banjos and
drumheads since 1958 due to its durability and acoustical properties when stretched over the bearing edge of the drum. They are made in single- and double-ply versions, with each ply being 2–10 mils (0.051–0.254 mm) in thickness, with a
transparent or
opaque surface, originally used by the company
Evans.
Clear and white boPET films are used as core layers and overlays in
smart cards.
Printing media
Before the widespread adoption of
computer aided design (CAD),
engineering drawings or
architectural drawings were plotted onto sheets of boPET film, known as
drafting film. The boPET sheets become legal documents from which copies or
blueprints are made. boPET sheets are more durable and can withstand more handling than
bond paper. Although "
blueprint" duplication has fallen out of use, mylar is still used for its archival properties, typically as a record set of plans for building departments to keep on file.
Used in dentistry when restoring teeth with composite
In
nail polish, as a coloured and finely shredded additive to create a glitter effect
Numismatics – Storing coins for long periods of time.
PVC was previously used for this, but over long periods of time PVC can release chlorine, which reacts with the silver and copper in coins. BoPET does not have this problem.
In fishing fly tying, metallized Mylar strips are sometimes wound around the hook shank for reflective striping or shimmer in certain patterns.
Military uniform accoutrements are often accented by gold mylar, such as shoulder epaulets or shoulder knots. For example: US Army Officer's Mess Dress Uniform.
^Eyes in the Sky, Dino A. Brugioni 2010, Naval Institute Press,
ISBN978 1 59114 082 5, pp. 102, 115.
^Staugaitis, C. & Kobren, L. (1966) "Mechanical And Physical Properties of the Echo II Metal-Polymer Laminate (NASA TN D-3409)", NASA Goddard Space Flight Center.
^Scott, Randall W. (1998). "A Practicing Comic-Book Librarian Surveys His Collection and Craft". Serials Review. 24 (1): 49–56.
doi:
10.1080/00987913.1998.10764429.
History of Polymers & Plastics for Teachers. by The American Chemistry Council
(HTML format) or
(PDF format) - 1.9MB, which includes the "
chasing arrow" recycling symbols (PET is #1) and a description of plastics.